Hello, I am a new tractor owner and have been having a great time blowing snow with my Kubota LX2610. The overnight low temperature last night hit -26C. We are now "up to" -22C and after 10 seconds of using the glow plugs to warm the cylinders, the tractor won't start. The engine turns over fine and is connected to a battery conditioner. How long is "safe" to warm the cylinders using the glow plugs? Thank you.